Re: [Xen-devel] [PATCH 08/18] arm/altp2m: Add HVMOP_altp2m_destroy_p2m.

[Sergej Proskurin <proskurin@xxxxxxxxxxxxx>]

Hi Julien,


On 07/05/2016 01:48 PM, Julien Grall wrote:
>
>
> On 05/07/16 12:37, Sergej Proskurin wrote:
>> On 07/04/2016 06:32 PM, Julien Grall wrote:
>>> Hello Sergej,
>>>
>>> On 04/07/16 12:45, Sergej Proskurin wrote:
>>>> Signed-off-by: Sergej Proskurin <proskurin@xxxxxxxxxxxxx>
>>>> ---
>>>> Cc: Stefano Stabellini <sstabellini@xxxxxxxxxx>
>>>> Cc: Julien Grall <julien.grall@xxxxxxx>
>>>> ---
>>>>    xen/arch/arm/hvm.c        |  2 +-
>>>>    xen/arch/arm/p2m.c        | 32 ++++++++++++++++++++++++++++++++
>>>>    xen/include/asm-arm/p2m.h |  3 +++
>>>>    3 files changed, 36 insertions(+), 1 deletion(-)
>>>>
>>>> diff --git a/xen/arch/arm/hvm.c b/xen/arch/arm/hvm.c
>>>> index 005d7c6..f4ec5cf 100644
>>>> --- a/xen/arch/arm/hvm.c
>>>> +++ b/xen/arch/arm/hvm.c
>>>> @@ -145,7 +145,7 @@ static int
>>>> do_altp2m_op(XEN_GUEST_HANDLE_PARAM(void) arg)
>>>>            break;
>>>>
>>>>        case HVMOP_altp2m_destroy_p2m:
>>>> -        rc = -EOPNOTSUPP;
>>>> +        rc = p2m_destroy_altp2m_by_id(d, a.u.view.view);
>>>>            break;
>>>>
>>>>        case HVMOP_altp2m_switch_p2m:
>>>> diff --git a/xen/arch/arm/p2m.c b/xen/arch/arm/p2m.c
>>>> index 6c41b98..f82f1ea 100644
>>>> --- a/xen/arch/arm/p2m.c
>>>> +++ b/xen/arch/arm/p2m.c
>>>> @@ -2200,6 +2200,38 @@ void p2m_flush_altp2m(struct domain *d)
>>>>        altp2m_unlock(d);
>>>>    }
>>>>
>>>> +int p2m_destroy_altp2m_by_id(struct domain *d, unsigned int idx)
>>>> +{
>>>> +    struct p2m_domain *p2m;
>>>> +    int rc = -EBUSY;
>>>> +
>>>> +    if ( !idx || idx >= MAX_ALTP2M )
>>>
>>> Can you please add a comment to explain why the altp2m at index 0
>>> cannot be destroyed.
>>>
>>
>> This has been adopted from the x86 implementation. The altp2m[0] is
>> considered as hostp2m and is used as a safe harbor to which you can
>> switch as long as altp2m is active. After deactivating altp2m, the
>> system switches back to the original hostp2m view.That is, altp2m[0]
>> should only be destroyed/flushed/freed, when altp2m is deactivated.
>
> Please add a comment in the code to explain it.
>

Ok, I will add an appropriate comment, thank you.

Cheers,
~Sergej


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